1. Field of the Invention
The present invention relates to a semiconductor layer annealing method and, more particularly, to a method of annealing a semiconductor layer, such as a silicon layer, formed on a substrate, such as a glass plate.
2. Description of the Prior Art
Most liquid crystal devices employ a substrate of low-melting glass having a softening point of 600.degree. C. because low-melting glass is inexpensive. In fabricating a liquid crystal device employing a low-melting glass substrate, a very complex LSI circuit must be formed on the low-melting glass substrate. In forming a LSI circuit on the low-melting glass substrate, a semiconductor layer, such as a silicon layer, is formed on the low-melting glass substrate by, for example, a CVD process, and then the semiconductor layer must be annealed.
Generally, the semiconductor layer is annealed by a lamp annealing process, in which the semiconductor layer is heated at an annealing temperature on the order of 600.degree. C. because it is possible that the low-melting glass substrate is deformed by heat if the annealing temperature is higher than 600.degree. C. It is possible to form a LSI circuit on the semiconductor layer annealed at 600.degree. C. and the characteristics of the semiconductor devices, such as transistors, of the LSI circuit are passable. However, an annealing temperature on the order of 600.degree. C. is unable to prevent the creation of traps in the semiconductor layer and traps produced in the semiconductor layer cause restraints on the improvement of the semiconductor devices formed on the semiconductor layer. The semiconductor layer must be heated at a temperature in the range of 1200.degree. C. to 1400.degree. C. for perfect annealing.
An annealing method proposed in Japanese Patent Laid-open (Kokai) No. Hei 2-11452 employs an excimer laser beam for annealing. The excimer laser beam is able to heat only the semiconductor layer effectively without heating the substrate. However, the energy of a pulse of an excimer laser beam emitted by an excimer laser available in the market is as small as 1 J. Therefore, it is difficult to anneal a semiconductor layer having a relatively large area with the excimer laser beam because the excimer laser beam is able to anneal only a very small section of the semiconductor layer at at time and hence the annealing cycle must be repeated many times for many small sections of the semiconductor layer. Thus, the throughput of an annealing apparatus using the excimer laser beam for annealing is very small.
An attempt has been made to anneal a semiconductor layer by scanning the entire area of the semiconductor layer with an excimer laser beam. However, if the semiconductor layer is scanned with the excimer laser beam, the portions of the semiconductor layer on the scanning lines and those of the same between the scanning lines may be heated respectively at different temperatures. Thus, it is doubtful if the method of annealing a semiconductor layer by scanning the semiconductor layer with an excimer laser beam is practically applicable.